Magnetic devices, such as transformers, motors, generators and the like typically include wound or layered core members composed of magnetic polycrystalline metal alloy. Alternatively, amorphous (i.e., noncrystalline, or glassy) magnetic metal alloys are now available for use in these devices. Such amorphous materials are described, for example, in Chen et al U.S. Pat. 3,856,513.
When used in wound cores, a continuous strip, ribbon,or tape of such a material is typically wound on a suitable mandrel and annealed to relieve winding stresses. The mandrel is then removed from the core, which is then cut and treated for receiving windings thereon.
One of the problems with magnetic core members of amorphous material formed according to the prior art processes is the core losses produced by the existence of voids, or spacing between the layers of the magnetic strips or tapes. Such voids increase transformer losses due to a low packing factor, i.e. reduced density of the magnetic core. This spacing effect, also known as the space factor, is more pronounced for magnetic tapes made from amorphous alloys since such materials may exhibit less cross-sectional rectangularity than the conventional crystalline tape material. For example, in the case of a transformer, the voltage (E) induced (or impressed) on a transformer winding is
E=4,44 BfNAS PA1 B=peak working density of core material PA1 f=frequency PA1 N=number of turns of winding PA1 A=cross-sectional core area PA1 S=space factor of core material
where:
The above formula shows that the induced voltage is directly proportional to the space factor, i.e., as the space factor decreases (from unity), the induced voltage decreases. The peak working density B cannot be increased since it is fixed at a given percent of saturation density. Since the power capacity of a transformer is a function of the impressed or induced voltage squared, reduction in space factor seriously impairs the power capacity of the transformer. This loss could be compensated by increasing the iron and copper contents of the transformer. However, a better alternative wound be to improve the space factor. This is an especially desirable alternative for magnetic cores wound from amorphous magnetic strips since substantial improvement is possible. In some cases, the space-factor for amorphous strips can be as low as in the order of 0.8, compared to the conventional polycrystalline strips (e.g. silicon iron composition) which can have a space factor as high as 0.97.